Closed tuned coil or loop aerial



Arrow/vir Dec. 29 1925- Dec. 29, l925- A 1,567,542 W. PICKARD CLOSED TUNED COIL OR LOOP ARIAL original Filed 'June so, y1921 :s sheets-sheet 2 INVENTOR ATTORNEY Dec. 29, 1925. 1,567,542 G. W., PICKARD CLOSED TUNED COIL OR LOOP AERIAL Original Fil'ed Jne 30, 1921 3 Sheets-Sheet INVENTOR l ATTORNE)I ramas nea ze; leas.'

A CGBPOBTION 0F NEW YORK.

MASSACHUSETTS, SSIGNOR BOSTON, MASSACHUSETTS,

CLSED TUND COIL OR L00? AERIAL.

l@riginal application led June 30, 1921, Serial No. 481,498. Divided and this application filed October 17, ieee.

To all 'whom t may concern."

Be it known that l, GRnnNnnAr 'Wiarrrrnn Prcim'iuna citizen of the United States of America, and a resident, of Newton Center, State of Massachusetts, have invented certain new and useful Closed Tuned Coil or Loop Aerials, the principles of which are set orthin the following specification and accompanying drawings, which disclose the form of the invention which l now consider to be the best of the various forms in which the principles of the invention may he embodied.

This is a division of my application, Serial No. 481,498, filed June 30, i921, and relates more particularly to the invention of Figs. 3 5 thereof which invention may be embodied to contain various features oi the other figures.

This invention relates to closed tuned coil 'or loop aerials for receiving and transmitting in radio communication and of the type of receivers known as direction finders or radio Compasses and of the type of transmitters for directional transmission. The present invention is an improvement over the invention disclosed in my Patent 876.996, granted January 2l, 1908.

The advantages of closed tuned loop aerials of one or more turns, such as disclosed in Patent 876,996 are now well known. Such aerials when used for receiving have sharply directionalproperties and are used extenswely for direction finding, as on ships and air planes, that is, for determining the location of a distant transmitter, and for the purpose ot' guiding and directing the ship or air plane. Such loops are also used for receiving signals and messages because, b v reason of their directional properties and sharp tuning, static and interference are in a large measure eliminated or reduced.

The theory of operationin receiving of such a closed tuned circuit as disclosed in my patent above-mentioned and disclosed in this application in an improved form is briefly Vas .follows: The electromagnetic waves set up by the distant transmitter cut the closed tuned loop or receiving aerial in the same manner that the lines of force generated around a primary of a transformer Serial No. 689,911.

cut the turns of the transformer secondary, setting up currents in the secondary circuit. ln like manner, the electromagnetic Waves in cutting the loop aerial, which is tuned to the frequency of the transmitted waves, set up oscillations in the aerial. The electromagnetic ux which cuts the closed tuned aerial increases with its enclosed area or turn area. A loop or closed aerial operating according to the above principle must be positioned with its plane in line with the distant transmitter in order to receive maximum signal or energy. ln aplane at right angles to the transmitter, the loop receives no energy :trom the transmitter nor is it a'eeted by it. The' voltage induced by the above :flux in a closed radio loop of the above character depends upon the enclosed area or number of turns. However, it has been found that such a closed circuit has more sharply directional properties, and is more eliicient if the resistance is a minimum. This means that the loop operates better without any resistance in series with it. Even a coupling' inductance as disclosed in F ig. 3 of the above-mentioned patent intro duces a certain amount or" resistance, and for this reason the loop is more eilicient it it consists of one turn rather than a number of turns, which increases the resistance of the loop. liurthermore, the conductor sistance of such a closed loop circuit should be as low as possible for optimum results in receiving or for direction finding. Finally, as the voltage generated in the loop circuit increases With the number of turns or inductance, while the current decreases in the same proportion.v I have found it advantageous to make the voltage low and the current high. A loop circuit closed through a condenser does not have all of its capacity localized in this condenser. By reason of the inevitable proximity of earth and other conducting objects, a certain amount of electrostatic capacity results from the conductor or` conductors of the loop to its sur,- roundings. If, as in a multiturn loop, the

condenser is of small value (because of the 100.

large inductance of a multiturn loop), this external electrostatic leld may be relatively large, and if the disposition of surrounding objects is` notl symmetrical, the d rectional :properties of the loop. are impaired. If the loop be made of minimum inductance,

that is, a. single turn, the capacity of the condenser' becomes large as compared-with the external electrostatic field, and the disturbingeilect of surrounding objects is minineicient e1ectrical1y,'and it also is not possible to obtain sharply directional properties on account of the small capacity necessitated by the high inductance. of the multiturn loop, as above explained. Also, the increased resistance due both tothe increased length of wire necessar for the multiple turns, and the increase high frequency resistance caused by the adjacent turns is wasteful of energy.

In such direction finders as are now in use,

the energy or oscillations set up in the coil are detected by means 'of a `detector circuit connected in shunt with the closed aerial'and in'shunt with the condenser in series with the aerial in the manner disclosed in Figcreased signal reception through high resistance and a certain loss in sharpness of directional characteristics by reason of the high loop inductance, as explained above,lthis lat'- ter disadvantage being quite serious when the loop aerial is used as a directionrinder or radio compass.

An ob`ect of t-h "invention is to provide a loop' aerial in which the eiiciency and directional properties are' increased.

Another object of the invention is to provide a loop aerial and detector circuit in which the electrical lconnection between thel two obviates the'use of long leads or resistbetween the loop, surrounding the receiving circuit to thedetriment of the ance-introducingcoupling coils such as have heretofore been used. A

Another object of the inventio'nis to ,pro-

' vide a closed loop aerial and receiving detecting-circuit in which electrostatictrouble's objects and means directional properties and efficiency of the loop are obviated.

Another object of the invention isto pro-l vide a compact, simple constructionof few parts `which may be easily handled and operated.

In the accompanying drawings, I have illustrated embodiments of my invention in which- Figure 1 is an elevation with parts in section of one feature with which the invention of Figs. 3 5 may be embodied;

Fig. 2 is a sectional plan view on the line 2-2 of Fi 1, looking in the direction of the arrows an on an enlarged scale;

Fig. 3 is an elevation of an el'nbodimentl of 'the invention;

Fig. 4 is a plan view thereof;

Fig. 5 is a detail sectional plan view on the line 5 5 of Fig. 3, looking in the direction of the arrows;

Fig. 6 is a sectional elevation of another feature with which the invention of Figs.

-3-5 may be embodied, and illustrated dagrammatically; and y Fig. 7 is an elevation, partly in section, of :mother feature with which the invention of Figs. 3-5 may be embodied and illustrated diagrammatically.

Referring to Figs. 1 and 2, I have illustrated a closed aerial circuit 1' which is completed through a static condenser system 2. This condenser system, which is in series with the closed loop, is made (because of the low inductance of the loop of the resent invention) in two parts 2a and v2b 1n parallel with each other and both connected or connectable in series with the loop l1. The part 2a comprises a'number of condensers, prefci'ablyI mica condensers, each having differ-l ent capacities and one and all being capable Aof being connected in series vwith loop 1. The part 2b is a variable condenser, and after the approximate resonant capacity value of the condensers 2 is obtained, the final 'tuning adjustment may besecured bythe variable condenser 2b.

@The condenser stem 2 comprises a metal casing C, Supporting the aerial 1, and provided at the bottom with a vertical tubular extension 3, rotatably supported in frame 4, ball bearings 5 being provided for easy turning, whereby the entire apparatus, in-l cluding t-he casing C, condensers 2 and the loop 1, may be rotated about a vertical axis for the purpose of properly positioning the same with reference to the distant tranmsitter. The lower end of the tube or sleeve 3 is rovided with an adjustin wheel or han le 6. The lip 1 is supported on casing C and insula therefrom vby bushin' 7 of any suitable insulating material aving vgood dielectric properties such as bakelite dilectoor quartz, the bushmgs being arranged at dlametrically opposite 'points in casing 2. The free ends of the loop 1 are inserted within these bushings 7 and project inside of the. casing C. Une end of the loop is provided with a metal segment 8 to which are electrically connected adjacent ends of the condensers 2a and 2b. Telescoping the tube 3 is a sleeve 9 provided at its lower end with an operating wheel o rhandle 10 and terminating at its upper end within casing 2 inan insulating plate 11 of suitable insulatmg and dielectricproperties. Secured to the upper surface of the insulating plate 11 is a metal plate or segment 12 adapted to engage contact fingers 13 (Fig. 2) Vupon the condensers 2a at the ends thereof remote from their points of connection to the segment 8. A contact linger 14 also engages the plate 12 and is electrically connected through conductor 15 within casing C to the opposite end of the loop, whereby `the circuit 1 is closed through one or more of the condensers 2a. Extending vertlcally,

through the sleeve 9 is an actuating rod 16 provided at its lower end with an operating handle 17 for operating the variable condenser 2b. rlhe upper end 18 of the rod 16 has secured to it the relatively adjust able plates 19 of the variable condenser 2b, which are interposed between the relatively fixed plates 20 of the variable condenser. The plates 2O are electrically Dconnected to segment 8, while the plates 19 are insulatedu from the rod 16 by suitable insulation 21. The relatively movable plates-19 are electrically connected by a'conductor 22 to conductor 15. l

By the above construction. it will be seen that in tuning the closed loop 1', one or more of the condensers 2EL may be successively thrown into series with the loop 1 by means ot the actu-ating handle 10 for securing rough adjustment and tuning ot the circuit 1 and the'tinal tuning and adjustment may be secured by rotating handle 17, thereby actuating and varying the variable condenser 2. By means of the handle 6, the entire apparatus may be properly positioned. .i coil 23, which with aerial 1 as a whole constitutes a. transformer and which may comprise a number of turns depending' on given conditions, is secured by means of an adjust-able collar 24 to the tube 3, this collar being adjustably clamped to tube 3 by anysuitable clamping means 25. By rotating the collar 24 around the sleeve 3 and thereby rotating coil 23, the inductive coupling between coil 23 and loop 1 may be varied for optimum effect. from coil 23 are electrically connected to any suitable detecting or transmitting circuit,

such as, for instance, an audion circuit@ j crystal detector clrcuit or any standard.;` celving laerlal c1rc111t and the detector or secondary clrcultdepends upon the resistance 'or damping of these circuits, and where the transmitting circuit, whereby the oscillattlons set up in the loop 1 are inductive-ly high frequency resistance low. In all cases The leads 26v transferred to transformer secondary 23 `and detected or whereby the reverse occurs most efficient form for this conductor is a circle of thin-walled copper tubing, as in Fig. 1, While for a loop of more than one turn a suitably stranded or braided cablev should be used (Figs. 6 and 7) tolkeep the 7 the loop should enclose suiiicient area to be operative under any given set of conditions. By way of example, only, such a ring or closed loop may have a diameter across the same of three feet, the diameter of the tubular part being about 2 inches,

and the thickness of walls about 1/'32 of an inch. Such construction, when properly tuned by the condenser system 2, constitutes a closed tuned circuit enclosing an area which, when its plane'is in line with the distant transmitter recives maximum current,j and when at rightangles to the transmitter, has a null point.` The copper tubing loo-p such as disclosed in Figs. l and 2 has minimum resistance, minimum inductance, maximum current and maximum capacity.

A singleturn loop. such as disclosed in Figs. l and 2 provides a closed circuit having high current and comparatively low voltage. This circuit 1 as a whole, by reason of the oscillations impressed upon itby the electromagnetic waves, acts in receivmg as a pri-A mary o-a transformer which is in inductive relation to the secondary of the transformer 23 secured to the tube 3 below it. This secondary 23 is connected up to any suitable receiving and detecting circuit as described above. The secondary 23 is adjustably secured to sleeve 3, and can be adjusted around sleeve 3 as an axis to vary the coupling between it and'coil 1. In the use of the apparatus,tl`1e coil 23 is adjusted until maximum response orgoptir'num response or signal lis obtained. Thereafter, by means of lthe' clamping screw 25, the coil l23 is fixed relatively to the loop 1,y and the whole, both coil 23 and loop 1, may be rotated' in accordancewith direction-finding practice.

An advantage vof the type of coupling between the closedl aerial 1 andthe coil V23 resides inthe fact that the coils 1 and 23 may be physically separated sufficiently so that*- separation between the circuits, which in turn minimizes the electrostatic effect. In constructions now 1n use in which the receiving circuit 1s connected by means of an 1nduc'tive coupling in series with the loop 1 or by leads such as above referred to, forming a detector shunt with the loop, the electrostatic effects are detrimental to the efliciency of thc circuit, because of the close coupling necessitated bythe relatively high circuit resistance. l

Asv is well known, the coupling between two coils ofy a transformer can be adjusted either by increasing the parallel separation between the coils, or by moving the coils transversely to each other, or by rotating one coil around an axis, whereby the angular position between the coils is varied. When the planes are parallel, we have maximum mutual inductance, and when the planes are at right angles, no mutual inductance. However, there is always an optimum position or coupling between the coils which can be easily determined by the operator for obtainin the loudest signal. This optimum coupling under any condition canbe obtained with the two coils 1 and 23 spaced suiciently apart to avoid electrostatic coupling.

Such an arrangement as above described, in which the closed aerial 1 as a whole constitutes a primary of an oscillation transformer and the coil 23 constitutes the secondary of the transformer, materially lowers the losses in the complete apparatus and ensures better tuning and eiliciency. The decreasing` ofthe resistance and inductance in the coil 1 ensures increased current and obviates the ne` cesity for a large number of turns in coil 1. The number of secondary turns of the trans` former 23 is large compared to the number of turns of the closed aerial whereby the the coil 1 and the secondary23 constitute a step-up transformer. This being the case,

there is no necessity for a large number of.y

turns in the loop 1 to generate the necessary voltage to operate the detector, this increased voltage being secured in the secondary 23 by the present invention. I

An advantage ofthe construction shown in Figs. 1 and 2 isthat the receiving circuit is of very low resistance because no coupling coil is used, nor-are A,there any long leads.

This permits the 'use of a single'uturn receiving lcoil, 'hence giving maximum eiiciency.l

Again, the directional properties of the sys-4 tem are extremely sharp, because the closed loop circuit 1 has no long leads or connec tions to any moreor lessg'rounded circuit, as'isthe case inthe ordinary modes of communicaton. `Furthermore, the system is exsubstantially treinelysimple beca-use it is not necessary, as

in the case of inductive couplings, toinseit an inductanoe in series with the loop, nor is it necessary to provide long leads to the de tector circuit.

'v As illustrated in Fig. 1, both the closed aerial or primary and the secondary coil 23 are mounted on the same frame, and if the apparatus is used on a single wave-length, the coupling may be made non-adjustable and xed ,byr the constructor at the bestl value. Oi?v course, it used on wide wave#y length ranges, the coupling between the coils 1 and 23 should be made variable in any suitable manner such as those enumerated above.

In Figs. 3, 4 and 5, I have illustrated a modified embodiment of the invention in which the numberv of movable and adjustable parts is reduced to a minimum and 431 and a second closed loop or circuit'32 having in series therewith an adjustable tuning condenser 33. These two loops 30 and 32 may be secured in fixed position to any suitable insulating support Y34 and are arranged in intersecting planes at right angles to each other as illustrated, the loops being circular and ofthe same size, having similar electricalcharacteristics, insulated from each other, and arranged s mmetrically relative to each other. -he closed aerials 30 and 32 may comprise any suitable conductive material or any number of turns, but, for purposes of illustration, I have shown the same as being composed of my tubular constructions such as disclosed in Fig. 1. Extending vertically along the line of intersection of the two loops 30 and 32 is a rod 35, journaled at :36 in the supnecessary voltage is developed for 'operating' Y the detector. In other words, 1n receiving,

port 34 and having a wheel or handle 37 at per end is a coil 38 comprising any suitable or sufficient number of turns for the purposes lof thislinvention, This coil 38 is arranged lwith,y its axis, on a line coinciding with theline-of intersection of the planes of the two loopsj30 and 32 and is arranged centrally and symmetrically of the two loops.

Leads 39 from the coil 38 may be connected i lto 'any suitable :receiving or detector circuit as above described or a transmitting circuit.

'whereby the direction may be determined.

Electrical oscillations 'set up from a trans- -ISecured to rod'35 above the handle 37 is a i initter at any point in a horizontal dplane will aiect the two aerials30 and 32 ierentially depending upon the location of the transmitter. However, wlienthe coil 38' is rotated, its position, when maximum response is noted in the receiver or telephone, indicates the position vof the distant transmitter, that is to say, when the maximum response is observed, the plane of the coil 38 will be in line with the distant transmitter. By the above construction, I ani enabled to obtain direction without necessitating the rotation of' the aerial or aerials.

Y former.

In'Fig. 6, I have illustrated another embodiment of the invention comprising a closed aerial or loop 45, which may consist of several turns of strandedowire wound upon a suitable insulating frame 46 and in series with which is an adjustable tuning condenser 47. Located within loop 45 is a secondary coil 49 consisting of suitable number of turns o wire, preferably exceeding the number of turns in aerial 45, being the equivalent of the secondary 23 illustrated in Fig. 1.. However, in the present embodiment of the invention,l the secondary 49 is illustrated centrally within the coil-.45 and parallel with the turns thereof, which is the position for maximum magnetic coupling. The secondary 49 may be adjusted for optimum coupling by rotating it around a vertical axis. The coil 49 may be connected through leads 50 to any desired form of detector or secondary circuit. The aerial 45 with coil 49 constitutes a transformer functioning according to the principles of the invention described above.

In F ig. 7, I have illustrated a form of my invention slightly modified from that of Fig. which comprises thev closedl tuned primary or loop aerial 5l comprising Several turns tuned by a variable condenser 52 in series with it. Coupled with this loop aerial .is a secondary coil 53 of a sufficient numberjofturns. Any desired variation of coupling may bc obtained by either moving the coil 53 axially away or towards the coil 51,or, as indicated by the double-headed vertical arrow, coil 53 may be either moved laterally across the face of coil 51 or rotated around an axis parallel with the doubleheaded arrow, to vary the coupling.-

The secondary circuit of'Fig. 7 including coil-53 is tuned by a variable condenser 54, and the radio 'frequency amplifier 55A is connected between this secondary l circuit and the indicator 56. In the form of Fig 7,

the diameter of the secondary 53 approxi- I mates or is of the order of magnitudeof that of the coil aerial 51, and such secondary 53, inasmuch as it is tuned to the frequency of .the primary 51, acts as a closed tuned coil aerial .to a certain extent, the current set up in y,coil 53 by the transmitted electro- 70 magnetic waves being added in quadrature to the currents transferred by induction from aerial 51 to coil 53. v

The main features of the above-described construction reside in the fact that the inductance and resistance of the closed aerial circuit is reduced to a minimum by reason of the omission of conductive leads and inductances inserted in series or in shunt in the circuit. The secondary coil with which the primary or closed loop aerial co-operates as a whole is sufficiently spaced to prevent electrostatic couplings, but at the same time is so adjustably coupled to the closed aerial as to receive maximum or optimum signal. 95 This arrangement increases the sharpness of directivity by an appreciable amount. By the above construction, increased current is secured in the coil aerial, which current is transferred directly from the coil aerial to a secondary of increased .number of turns,

whereby the required E. M. F. is-generated in the secondary.

In short, my invention comprises a closed aerial circuit, coupled inductively to a coil of a detecting or transmitting circuit, the two constituting the primary and secondary of an oscillation transformer.

A form of the present invention which I have used consisted of 33 turns of 3/8 inch 100 Belden high frequency cable wound as a single layer solenoid on a' square frame 44 inches on a side. This loop aerial with its associated tuning condenser, and when coupled` to a detector lcircuit for maximum 305 signal,had the extremely low resistance of 1.2fohms at a wave length of 12,500 meters. Good signals were received from European, stations, and, owing to the low resistance of the loop aerial, very sharp timing was possible.

It is to be understood that the invention is not limited to the embodiments and teatures specifically shown and described herein, but that such embodiments. and features are subject to changes and modifications without any departure from the spirit of the invention.

I claim 1. Radio directional-loop aerial receiving apparatus comprising two` loop aerials operatively and permissively fixed in vertical planes at substantially right angles to and intersecting one another, said aerials thereby permitting production by transmitted Waves, of a magnetic field the direction of which coincides with that of such waves; and a rotatable pick-up coil located insaid ma eti fi ld, acting 'as a secondary to sait loop aerials as a whole as a primary,

and affected4 by -said 'field save when y,in a.

substantially the same enclosed area andIl permissively operatively ixedv in vertical planes at substantially right'angles to and centrally intersecting Vone another, said aerials thereby .jointly permitting the pr0- duction, by transmitted waves, of a magnetic eld the direction of which coincides with-that of lsuch waves; anda rotatable` pick-up coil located on the line thru the central intersection of said'loop aerials and acting as a secondary tov said loop aerialsv as a'whole as a primary, whereby the position of the pick-up coil determines the direction of the distant source of such waves.

3, RadioV directional-loop aerial receiving apparatus comprising two loop aerials each 'of substantially the same enclosed area and each consisting of Va single turn .of metal tubing of low resistance, said two aerials being permissively operatively 'fixed in vertical planes at substantially right angles to and centrally intersecting one another, said aerials thereby jointly permitting the production, by transmitted waves, of a magnetic field .within them generally on the line of their intersection, the direction of which field is that of such waves; and a rotatable pick-up coil located centrally withinv said two aerials' and having relatively smallarea and consequently low electrostatic capacity with respect to said aerials and consequently only slight disturbing effect on the aerials, said pick-up coil acting as a secondary to said loop aerials as a whole as a primary. GREENLEAF WHITTIER PICKARD. 

